Electric oven for the burning of ceramic articles



y 13, 1954 K. HINTENBERGER 2,678,958

ELECTRIC OVEN FOR THE BURNING. OF CERAMIC ARTICLES Filed Dec. 4, 1951 INVENTOR. KARL HINTENBERGER ATTORNEY Patented May 18, 1954 ELECTRIC OVEN FOR THE BURNING OF CERAMIC ARTICLES Karl Hintenberger, Vaduz, Liechtenstein Application December 4, 1951, Serial No. 259,855

Claims priority, application Switzerland December 8, 1950 11 Claims.

The present invention relates to an electrically heatable furnace for burning ceramic articles, and more particularly for burning artificial teeth.

Broadly, the invention provides aheatable furnace comprising at least one heating chamber and means for substantially evacuating the heating chamber or chambers; a substantially cylindrical enclosure; means for closing the enclosure airtightly, including a door-like closure member formed by one of the circular end walls of the cylindrical enclosure; an outer lining of loosely stacked blocks of refractory material p sitioned in the enclosure and enclosing a central heating chamber, the heating chamber being formed of two side walls having a plurality of longitudinal grooves, a back wall, a plurality of ceramic plates carrying electrical resistance elements and being slidably held in said grooves, a top plate of ceramic material being slidably held in the uppermost of the grooves; and a removable ceramic. member placed between the heating chamber and the closure member, the electric resistance elements of each of the plates being connected separately with lead-in wires including conductors placed between the loosely stacked blocks of the outer lining.

It is preferable, in accordance with the invention, to arrange the furnace enclosure as a double- Walled cylinder forming a jacket which may be connected to a vacuum pump by means of an air pipe so that the jacket may be independently evacuated, or its air pressure reduced without interfering with the pressure in the burning chamber. For this reason the connection of the jacket and of the burning chamber with the vacuum pump is preferably such that the suction pipe and the admission pipe unite only directly before their entry into the furnace enclosure, whereby both conduits may be closed independently of each other by means of valves, shutters, or the like.

One may provide the individual blocks or bricks with designations such as marks or notches, raised or countersunk signs or the like, by means of Which their position in the oven can be determined and whereby their assembly can be made to follow a certain plan of construction. As a further improvement the said blocks or bricks may be provided with bore holes or other excavations which may unite into channels or passages into which the electric wires for the heating elements, may be concealed or for the accommodation of instruments such as thermostats or any other devices which may be found useful in the operation of the oven.

The carriers for the heating elements are preferably fluted plates carrying electric resistance elements connected to a source of electricity by lead-in wires in such a manner as to be able to connect and disconnect the elements in the said plates, or to regulate their heating capacities, independently of each other or in groups.

The accompanying drawing illustrates a construction of the oven and of a heating plate in accordance with the invention by way of example and in conformity with the also illustrated diagrams of heat-distribution in the burning chamber. in this sheet of drawings:

Fig. l is a perspective View, partly broken away, of the burning oven showing the outer casing, the lining, the heating plates, the electrical connections and the vacuum The closin stones are shown removed and placed separately outside the oven entrance.

Figs. 2 and 3 are temperature diagrams obtained by measuring the temperature in the 1ongitudinal mean and in the transverse mean of the oven when heated by heating plates with an even istribution of like heating resistances.

Fig. c is a diagrammatic top View upon one of the heating plates with its heating resistances in a partly broken away perspective view.

In these figures the numeral 1 is used to denote the door or cover of the even, which may be made of an iron plate for example and reinforced by a circular rib 2 which is grooved for the reception of a packing 3. This packing, which may be made of rubber or any other suitable material, is adapted to be pressed against the annular face of the cylindrical shell l. An appropriate closure, which is not shown in the drawing and which may be of any known or convenient kind, serves to hermetically seal the door 1 upon the oven during the operation period of the latter. The inner cylinder Q, which may be made of sheet iron for example, is concentrically surrounded by the external shell 5, and both these cylindrical shells i and "5 are airtightly united as by Welding to a common back wall 6. At their front the two cylinders i and ii are joined by the annular plate i also welded thereto. The cylinders in conjunction with their end plates 5 and 1 enclose the hollow jacket 3 between them. Loosely stacked. in the inner cylinder are the insulating blocks or bricks 9, Which consist of porous refractory material such as fire clay, crucible or other suitable material with the usual addition of lean clay or the like. Corresponding to the cylindrical shape of the inner shell the said blocks or bricks are individually shaped so that they may be more easily inserted at their proper places and to thus form the burning or heating chamher [0. Along its sides the burning chamber is flanked by plates ll. These plates also consist of fire-proof material, such as steatite for example, and they are provided with longitudinal grooves l2, serving as guides or runways for a number of horizontally superposed parallel plates l3 adapted to be slid into and along the grooves l2 from the front of the oven, which applies also to the top plate Mthereof. The plates l3, of

which there may be any desired number, are provided with longitudinal channels of originally circular cross section. These channels are disposed parallel to each other and they are in communication with the burning chamber by means of longitudinal slots It. In these channels the heating resistances I! are accommodated. Plate l4, however, does not contain any such passages or channels nor any kind of heating elements. As will be seen from Fig. 1 of the drawings, the plates i 3 together with the top plate l4, the back plate is and the closing stone I 9 enclose a number of individual burning compartments within the space of the general burning chamber is. The heating resistances I! are provided with connecting rods 28 which are joined to the leadingin wires 2i. The connecting wires in th oven are preferably accommodated in vertical notches or slots, or in the spaces between the refractory blocks forming the lining.

Bushes 26 which are also airtightly insulated are screwed into the back wall of the casing and serve for the connection of the leading-in wires outside of the oven.

At its front or charging end the burning chamher, which at this place is not subdivided by walls or heating plates, is closed by the stone l9. This stone may consist of a single fire brick or it may be composed of several such bricks formed preferably of the same material as the refractory lining of the oven. If several stones are used they are provided with drill holes 21 through which a screw or bolt 23 may be passed for holding the stones together by means of nuts 25 and Ma applied to their screwthreaded ends.

A vacuum pump 29 is arranged outside the oven, from which an air conduit 28 leads with a branch pipe into the interior of the burning chamber, while the pipe itself continues into the jacket 8 formed between the two cylinders 4 and 5. A shut-off valve 30 serves to close the jacket 8 to the line 28 and the pump 29. The air admission pipe 31 arranged at the top of the oven leads with its branches 32 and 33 also into the jacket 8 between the two cylinders 4 and 5 and into the burning chamber Ill respectively. Each of these branchv lines 32 and 33 is adapted to be closed by means of the valves 34 and 35 respectively, so that both chambers 3 and II] can be vented separately, thereby to reduce, or abolish, the under-pressure which may prevail therein. Branch 32 of the admission pipe 31 is provided at its end with a strainer 36, which prevents parts of dislodged material, such as may have entered the admission pipe via the vacuum line, to be blown into the burning chamber. There is, further, provided between the refractory bricks; and the inner shell 4 and enlarged space 31 at the entrance line of the branch conduit 32, which serves for enabling a quick distribution of the incoming air over as large a surface as possible.

As shown in Fig. 4 the heating resistances IT in the channels l5 of the plates I3 are arranged so that the number of windings in the successive coils is larger at the sides of the plates than at the centers thereof. In order to facilitate the understanding of the arrangement, the illustration of Fig. 4 shows the individual resistances in a diagrammatic way to be drawn out into sections of different length. In the practical embodiment of the invention there will be no such sections and the individual heating elements will be consecutively wound with only a lesser number of windings in the middle than at the sides of the plates. In the diagrams illustrated in Figs. 2

4 and 3 of the drawing, that shown in Fig. 2 cor-' responds to the temperature as measured in the longitudinal direction, and Fig. 3 to the temperature measured in the transverse direction,

gressively develop a greater heat at places where the loss of heat progressively increases, a practically uniform rise of temperature at all cross sections of the oven will be obtained.

As an example, the number of windings in the first third of the two outer resistances may be 10, in the center it may be 5, and 6 in the last portion, because the loss of heat during the opening of the oven is greatest at the front end, while at the back there is a loss due to the back wall taking up a certain amount of heat. So the loss in the back portion is greater than in the middle, but smaller than in the front portion. In the next-following resistances the number of windings may, for example, be 7 at the front and back, and 5 in the middle, because the loss of heat in the more inwardly located regions by the side walls is less than in the outer resistances. In the center of the heating plate the number of windings of the resistance may be 5 in the front and back, and e in the center. It must be understood that these figures are only given as examples and that the distribution of the resistances and the number of their windings may always be chosen to suit requirements.

What I claim. and desire to secure by Letters Patent of the United States is:

1. In an electrically heatable furnace comprising at least one heating chamber and means for substantially evacuating said chamber or chambers; the combination of a substantially cylindrical enclosure; means for closing said enclosure air-tightly including a door-like closure member formed by one of the circular end walls of the cylindrical enclosure; an outer lining of loosely stacked blocks of refractory material positioned in said enclosure and enclosing a central heating chamber; said heating chamber being formed of two side walls having a plurality of longitudinal grooves, a back wall, a plurality of ceramic plates carrying electrical resistance elements and being slidably held in said grooves, a. top plate of ceramic material being slidably held in the uppermost of said grooves, and a removable ceramic member placed between the heating chamber and the closure member, the electric resistance elements of each of said plates being connected separately with lead-in wires including conductors placed between the loosely stacked blocks of the outer lining.

2. In an electrically heatable furnace comprising at least one heating chamber and means for substantially evacuating said chamber or chambers: the combination of a substantially cylindrical furnace enclosure formed by two coaxial cylinders, a substantially circular end wall airtightly joined to the two cylinders at one end, an annular wall airtightly joined to the two cylinders at the other end, an annular airtight chamber being formed between the two cylinders, the circular end wall and the annular wall, and

a closure member forming a door at the other end of the two cylinders; an outer lining of loosely stacked blocks of refractory material positioned in said enclosure and enclosing a central heating chamber; said heating chamber being formed of two side walls having a plurality of longitudinal grooves, a back wall, a plurality of ceramic plates carrying electrical resistance elements and being slidably held in said grooves, a top plate of ceramic material being slidably eld in the uppermost of said grooves, and a removable ceramic member placed between the heating chamber and the door, the electric resistance elements of each of said plates being connected separately with lead-in wires including conductors placed between the loosely stacked blocks of the outer lining.

3. An electrically heatable furnace comprising, in combination: a substantially cylindrical fur nace enclosure formed by two coaxial cylinders, a substantially circular end wall airtightly joined to the two cylinders at one end, an annular wall airtightly joined to the two cylinders at the other end, the circular end wall and two cylinders and the annular wall forming an airtight annular chamber therebetween, and a circular closure member forming a door at the other end of the two cylinders; an outer lining of loosely stacked blocks of refractory material positioned in said enclosure and enclosing a central heating chamber; said heating chamber being formed of two side walls having a plurality of longitudinal grooves, a back wall, a plurality of ceramic plates carrying electrical resistance elements and being slidably held in said grooves, a top plate of ceramic material being slidably held in the uppermost of said grooves, and a removable ceramic member placed between the heating chamber and the door, the electric resistance elements of each of said plates being connected separately with leadin wires including conductors placed between the loosely stacked blocks of the outer lining and also being separately connected to heat control means; and means including air supply and air evacuation conduits for changing the air pressure in said airtight annular chamber and in said enclosure independently of each other.

4. Furnace as defined in claim 3, wherein said furnace enclosure is of metallic material.

5. Furnace as defined in claim 3, wherein said last-named means comprises a vacuum pump.

6. In an electrically heatable furnace comprising at least one heating chamber and means for substantially evacuating said chamber or chambers: the combination of a substantially cylindrical enclosure; means for closing said enclosure airtightly including a door-like closure member formed by one of the circular end walls of the cylindrical enclosure; an outer lining of loosely stacked blocks of refractory material positioned in said enclosure, the shape of the individual blocks being such that, when stacked in the enclosure, the lining has a circular periphery and confines a central chamber of substantially rectangular cross section; a heating chamber in said central chamber formed of two side walls, a plurality of ceramic plates carrying electrical resistance elements, means for removably holding said plates on said side walls one above the other, whereby the heating phamber is subdivided into a plurality of heating compartments, a back wall, a top plate of ceramic material removably held in the uppermost of said holding means in the side walls, and a removable ceramic member placed between the heating chamber and the door-like closure member; a source of electricity and heat-control means arranged exteriorly of said enclosure; and conductors connecting the electric resistance elements of each of said plates separately to the source of electricity and heatcontrol means.

7. Furnace as defined in claim 6, wherein the shape of the individual blocks of the outer lining is such as to leave room therebetween and between the lining and the enclosure for furnace fittings and electrical conductor means.

8. in an electrically heatable furnace comprising at least one heating chamber and means for substantially evacuating said chamber or chambers: the combination of a substantially cylindrical furnace enclosure formed by two coaxial cylinders, a substantially circular end wall airtightly joined to the two cylinders at one end, an annular wall airtightly joined to the two cylinders at the other end, an annular airtight jacket being formed between the two cylinders, the circular end wall and the annular wall, and a closure member forming a door at the other end of the two cylinders; an outer lining of loosely stacked blocks of refractory material positioned in said enclosure, the shape of the individual blocks being such that, when stacked in the enclosure, the lining has a substantially circular periphery and confines a central chamber of substantially rectangular cross section; a heating chamber in said central chamber formed of two side walls, a plurality of ceramic plates carrying electrical resistance elements, means for removably holding said plates on said side walls one above the other, whereby the heating chamber is divided into a plurality of heating compartments, a back wall, a to plate of ceramic material removably held in the uppermost of said holding means in the side walls, and a removable ceramic member placed between the heating chamber and the door; a source of electricity and heat-control means arranged outside of said enclosure; conductors connecting the electric resistance elements of each of said plates separately to the source of electricity and heat-control means; and means including air supply and air evacuation conduits leading into said jacket and into the interior of the enclosure for changing the air ressure in said jacket and in said enclosure independently of each other, the shape of the individual blocks of the outer lining being such that room is left therebetween and between the lining and the enclosure for said conduits and electrical conductor means.

9. Furnace as defined in claim 8, wherein said furnace enclosure is of metallic material.

10. Furnace as defined in claim 8, wherein said means for changing the air pressure in the jacket and in the enclosure comprises a vacuum pump.

11. Furnace as defined in claim 8, wherein the heating capacity of said electrical resistance elements diminishes in the direction from the walls of the heating chamber toward the center thereof.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 589,048 Timme Aug. 31, 1897 596,696 Custer Jan. 4, 1898 896,413 Reid Aug. 18, 1908 1,533,266 Reid Apr. 14, 1925 1,732,917 Summet Oct. 22, 1929 2,145,324 Stauss et a1 Jan. 31, 1939 2,210,483 Feron Aug. 6, 1940 2,279,511 Gottignies et a1. 1-", Apr. 14. 1942 

